Anastomoses of transverse tubules with terminal cisternae in polymyositis
S. M. Chou, I. Nonaka and G. F. Voice
Abnormal transverse or T tubules spatially continuous with sarcoplasmic
reticulum (SR), as visualized with a lanthanum (La) tracer, were found in
biopsy specimens from nine patients with polymyositis whose serum enzyme
(creatine phosphokinase [CPK]) levels were elevated before the time of
biopsy. On comparison with the T system in more than 50 control subjects
without CPK elevation, it became apparent that presumed anastomoses of T
tubules with SR were the most consistent anatomical correlates of the
enzyme leakage. Two types of anastomoses were seen on the basis of passage
of La: first, early segmental dilation of T tubules and perpendicular
continuations with SR; and second, focal proliferation of T tubules forming
"T tubule networks" and then anastomosing with SR at the periphery of the
networks. The latter is considered to be a concurrent repair process for
the injured triads. Lanthanum did not penetrate freely through the plasma
membrane of necrotized muscle fibers. It is concluded that junctional sites
between T tubules and SR may be the primary sites of leakage of
sarcoplasmic enzymes in polymyositis.
